Rep. James Lankford is a wonky, self-proclaimed “skinny redhead” with a voice as deep as a bullfrog, and now he’s running for Senate in the shadow of a giant of conservative politics, retiring Sen. Tom Coburn.

Lankford, an Oklahoma Republican, came to Capitol Hill in the tea party wave of 2010, joining his freshman class in voting dozens of times to dismantle Obamacare and ripping the level of debt and deficit spending during appearances on Fox News. In an interview with TIME on Tuesday just a day after launching his bid to succeed Coburn, Lankford said his top policy priorities include taking steps to eliminate government waste, reforming the Social Security disability benefit and working on energy development programs. And Lankford is no career politician: Before running for Congress, he ran a huge Christian youth camp.

But in the day since he announced his Senate bid, a host of non-establishment conservative groups—including The Madison Project, the Senate Conservatives Fund and Tea Party Patriots—have ripped Lankford as insufficiently conservative and a leadership “yes-man” in his role as House Republican Policy Committee Chair.

“He’s doesn’t buck the system; he doesn’t hold the line” said Matthew Vermillion, an Oklahoma tea party activist who, like some conservative leaders, prefers freshman Rep. Jim Bridenstine, should he decide to run.

“He’s voted three times to raise the debt ceiling,” Vermillion said of Lankford.

Lankford defended himself from many of the conservatives’ attacks, which have included scorn over his approval of the recent bipartisan budget compromise that averted a government shutdown, his openness to a path to citizenship for immigrants in the country illegally, and his opposition to an amendment that would have blocked funding for the NSA program that collects massive amounts of Americans’ telephone records. Lankford said he backed the budget deal that passed the House last month to protect the Pentagon from automatic spending cuts that otherwise would have taken effect. “I’m very, very pro-defense,” he said. But Lankford ultimately opposed implementation of that very budget bill by voting against an appropriations measure stipulating how the $1.1 trillion would be doled out across the government, citing $18 billion in waste.

On some issues, Lankford has yet to specify why he bucks the most conservative members of his party. When it comes to immigration, Lankford said there are “things that do need to be addressed” and that the system is “not working well,” as the number of immigrants in the country illegally has increased to about 11 million. Lankford said “we need to do major reforms to NSA” which are “long overdue,” but that the narrowly targeted funding amendment he opposed “doesn’t resolve it” to his liking. Lankford does support a citizen advocate on the secretive Foreign Intelligence Surveillance Court, which approves wiretaps and other intelligence activities.

“The challenge that we have is with some of the groups that are trying to define you based upon a single vote that was not comprehensive for what I really believe,” Lankford said. “That makes it really tough.”

Rep. Tom Cole (R-Okla.), an ally of House leadership, said criticism from outside groups may not be much of a factor in the race.

“I don’t think these third party groups are going to decide who Oklahoma Republicans are going to nominate,” Cole told TIME. “They’ve got a prism they look at the world through. I don’t think it’s the same prism that Oklahoma voters look at the world through.”

“Not being flippant, the outside groups really haven’t been involved in Oklahoma,” said Lankford, noting he defeated a Republican candidate backed by the conservative Club for Growth in his 2010 primary.

Cole said Lankford may have a bigger problem on his hands: Cole’s former staffer T.W. Shannon, the state’s 35 year-old House Speaker and a rising Republican player. Cole said he would be “very comfortable” with either candidate, but he also called Shannon, who is reportedly considering a run, an “emerging national star.”

“The two of them have overlapping donor networks, overlapping support networks, common friends,” Cole said. “I’m not painting this as tragic, because we’re going to have a great United States Senator out of this.”

In his campaign, Lankford will strive to separate himself as a solutions-oriented dealmaker in a time of gridlock in a town of shutdowns, posturing and fierce passions. Within the first two minutes of the interview, Lankford said one of the reasons he’s excited to move from his relatively high position in the House to be a backbencher in the upper chamber is that, as a senator, he can delve into the research necessary to solve problems with an expanded staff. He also believes his temperament is well suited to the Senate.

“Personally and politically I’m extremely conservative for who I am, but I’m also very careful in my tone,” Lankford said. “I don’t believe just because you’re a conservative that you’re angry. I can be plenty frustrated and not have to constantly portray myself as upset and angry at the world. I want to be very consistent in the message, because I really do believe that conservative solutions will work.”